554 CAROLINE BURLING THOMPSON 



cerebral lobes and may represent the efferent fibers or the motor 

 system of the head; the other root, ventral in position, the pos- 

 terior root of the mushroom body, continuing backward to the 

 protocerebral lobes, subesophageal ganglion, and ventral nerve 

 cord, may represent the effereot, motor system for the body. 

 To carry the comparison frequently made with the vertebrate 

 brain a step farther, if the mushroom bodies can be compared 

 with the cerebrum, the posterior root fibers may be likened to 

 the pyramidal tracts of the spinal cord. This explanation is 

 founded on facts to be observed in any series of sections of the 

 ant brains described in this paper, and it also supplies, in my 

 opinion, the missing factor in the entire continuity of the nervous 

 S3^stem of the ant. 



Any conception of the special function of the central body 

 seems far from clear. Here is a small highly differentiated or- 

 gan, constant in structure, in position, and in its occurrence in 

 all castes and genera of ants. It is connected by fibers with 

 the ventral part of the protocerebral lobes and with the roots of 

 the mushroom bodies. By these connections the central body 

 must be in direct communication with the chief centers of the 

 brain, but the question of its functional relation to these centers 

 remains as yet unanswered. 



COMPARISON OF THE BRAINS OF THE CASTES 



In comparing the brains of the different castes and genera of 

 ants, the question arises : Which is the generalized primitive type? 

 Most writers are agreed that the worker brain is more highly 

 developed than that of the queen. Wheeler, on the contrary, 

 dissents from this view on the ground that many queens are as 

 highly developed as the workers. On page 55, speaking of the 

 \aew of Forel that the mushroom bodies are larger in the worker 

 than in the queen, Wheeler refers to a series of Formica glacialis 

 (fig. 29), showing that: 



The pedunculate bodies (p. 6) are as highly developed in the female 

 as they are in the worker, and they can hardly be said to be vestigial 

 in the male. In Pheidole instabilis (fig. 30), too, the female and soldier 

 have well developed pedunculate bodies, though these seem to be insig- 



